Imaging System:

Understanding the brain

New imaging techniques are promising to reveal more about neural connectivities in the brain than ever before. See how Misha Ahrens, Philipp Keller and colleagues use lightsheet microscopy to visualize intact, living zebrafish brain in real time. Read now.

THE QUESTION

How do newly made neurons integrate into the adult brain?

Regions of the mammalian brain are constantly being remodeled through the incorporation of newly formed neurons, even in adult brains. How do these new neurons come on-line? What existing neurons do they connect with and how does link-up proceed?

THE BARRIERS

Tracking neural connectivities had been challenging, until the 2007 development of a pseudotyped rabies virus (RABV). Wildtype RABV is transmitted from neuron to neuron via synapses, and can easily travel to multiple neurons. Wickersham, et al,1 developed a mutant RABV that was missing the proteins needed for transmission across the synapse, thus controlling the spread. By initially infecting a small population of neurons with the RABV mutant, and supplying the missing proteins in trans, Wickersham, et al,1 were able to limit the spread of the virus to a single round, allowing identification of the neurons immediately connected to the initial cell.

Subsequent researchers took advantage of this construct to identify the partners of newly developed neurons in the dentate gyrus (DG) and olfactory bulb (OB) of adult mice, but did not investigate connectivity in the early stages of integration.

Deshpande, et al,2 adapted the RABV-based monosynaptic tracing technique to target adult-generated neurons for primary RABV infection. Using a Hamamatsu ORCA-R2 camera to detect neurons via infrared wavelengths, they were able to show that newly formed neurons in both the DG and OB integrate first into the local circuit before being incorporated into long-range connections, and suggest that integration may involve a similar sequence of events in other parts of the brain.

THE POSSIBILITIES

Deshpande, et al,2 took advantage of new technology to generate novel insights into a long-standing question. Learn about how even newer lightsheet microscopy technology, supported by Hamamatsu’s ORCA-Flash4.0 camera and pioneered by Misha Ahrens, Philipp Keller, and colleagues, is poised to shed even more light into how the brain works—read Seeing the Living Brain.